It's possible to over-practice a particular lick. You can get to the point where your muscle memory has the lick so drilled in, that playing some other lick that starts with the same movements becomes really difficult.

Most people, I think, would prefer to have a general skill, where that lick and other licks like it come easily to the fingers. That doesn't mean you shouldn't practice that lick - but I think variety is useful. Perhaps break your lick into smaller parts, practice them in isolation, and practice assembling them in different orders, along with different parts.

I personally find that if I abandon a part for a few days, when I come back to it I'm better than when I left it. The time off seems to allow the practice to bed-in.

As Dr Mayhem says, though - everyone's learning style is different. Find out what works for you.

I notice that as I practice something, my muscle memory gets better and better, but if I practice a lick for too long, I actually start forgetting what I'm doing and start getting worse at the lick. At that point, I switch to something else for a bit before coming back to the lick I was practicing. If this happens to you, then this might be a good strategy.

I would recommend a combination. Practice the lick in isolation at a tempo that you know you can play it 100% perfect. Then slowly increase the tempo. When you do, make sure you add the part of the song just before and after the lick that is troubling, so you have the context of the song, and the relative tempos of what you're having trouble with.

Another suggestion (along with the other good answers here), your mileage may vary, that's helped me get out of a particularly troubling passage, is to deliberately change the rhythm of the passage. For example, if it's a run of 16th notes, change it to be a syncopated rhythm, (e.g.: dotted eighth + sixteenth) and try it again. Then, reverse the syncopation. (e.g.: sixteenth + dotted eighth)

This technique is helpful in working out any physical problems with "getting my fingers to move like that". Of course, you don't want to practice it entirely this way, but merely to allow your fingers to get used to moving to those positions in that order.